This invention relates to a photo-semiconductor module.
When it is attempted to put a photo-semiconductor module into practical use which is constructed by optically coupling a photo-semiconductor device such as a laser diode (LD) or a photodiode (PD) to an optical fiber, since a photo-semiconductor device or some other part is sometimes deteriorated by an influence of an ambient humidity or the like, such construction is normally employed wherein the photo-semiconductor device and so forth are accommodated in an airtight sealed condition in a casing. Then, in the construction, it is necessary to optically couple such photo-semiconductor device to an optical fiber communicating with the outside of the casing such that the airtight condition of the inside of the casing may not be damaged. Thus, photo-semiconductor modules are demanded which assure a high airtight condition and are easy to produce.
Construction of an exemplary one of conventional photo-semiconductor modules will first be described with reference to FIG. 1.
A ceramic substrate 11 having a platform 11a at a portion thereof is secured to an inner face of a bottom wall of a casing 10 by means of solder 12. A PD (photodiode) chip 13 is secured by solder 12 to an upper face of the ceramic substrate 11 with a photodetecting surface thereof directed upwardly. Various other electronic parts 14 such as ICs and chip capacitors are also secured to the upper face of the ceramic substrate 11 by means of solder 12. Terminals 15 for supplying a power source to the parts 14 and for extracting a signal produced by photoelectric conversion at the PD chip 13 are secured to a side wall of the casing 10 such that an end of each of them may be positioned in the inside of the casing 10 and the other end may be positioned outside the casing 10. The PD chip 13 and the parts 14 on the ceramic substrate 11 are individually connected to the terminals 15 by way of bonding wires 16.
A tubular member 17 extends through another side wall of the casing 10, and an optical fiber 18 is inserted in the tubular member 17. The optical fiber 18 includes a bare fiber 18a and a nylon coating 18b coated on an outer periphery of the bare fiber 18a. The nylon coating 18b is removed at an end portion of the optical fiber 18, and gold 19 is deposited on a surface of the thus exposed bare fiber 18a by vapor deposition. The bare fiber 18a is polished obliquely at an end 18c thereof as shown in FIG. 1 and is secured at a side portion (at which the gold 19 is deposited) thereof to the platform 11a of the ceramic substrate 11 by solder 20 such that the end 18c thereof may be positioned above the PD chip 13. The bare fiber 18a is further secured to an inner end portion of the tubular member 17 by means of solder 21. The inner portion of the tubular member 17 is thus sealed in an airtight condition by the solder 21. A lid 22 seals an upper portion of the casing 10 in an airtight condition. The photo-semiconductor module is thus designed so as to prevent possible deterioration of the PD chip 13 and so forth with such construction as described above.
However, according to the conventional photo-semiconductor module of the construction described above, when the optical fiber is inserted into the tubular member and secured in position by soldering, the end portion of the bare fiber is likely to touch with the PD chip or other harts to cause damage thereto or damage to the PD chip. Since the gold is deposited on the side portion of the bare fiber by vapor deposition and the end portion of the bare fiber is necessarily be polished obliquely, if such damage occurs, then vapor deposition or polishing must be performed again. Accordingly, there is a problem that a comparatively large number of man-hours are required for such operation.
Further, an operation for the coupling between the optical fiber and the photo-semiconductor device and another operation for the airtight sealing must be performed simultaneously. However, since the two operations require high precision, there is another problem that an airtight sealed condition may not be achieved with certainty.